This invention relates generally to high pressure valves and particularly to bonnet securing systems for high pressure control valves.
It is common practice to provide a valve body with a removable bonnet that is maintained in a captivated relationship with the valve body stem mount by means of a bonnet nut. The bonnet is generally cylindrical as is the valve body stem mount, and an O-ring or the like provides the seal between the bonnet and stem mount. A shoulder on the bonnet is engaged by a bonnet nut that is threaded on the end of the stem mount. The bonnet nut may be of the hammer lug type, i.e. have a pair of external lugs to facilitate removal and tightening thereof in heavy duty installations.
A problem that often arises, usually after years of field service or service with corrosive medium fluids, is that the bonnet sticks in the stem mount and is not easily removable when the bonnet nut is removed. Should the valve body be inadvertently left under pressure, a dangerous situation may arise, since the stuck bonnet may suddenly be blown loose when the bonnet nut is removed. A prior art solution to the problem of removing a bonnet that is stuck in the stem mount is shown in FIG. 1, where a partial sectional view of a bonnet nut and a valve body is shown. A hammer lug type bonnet nut 10 having a pair of lugs 16 engages a shoulder portion of a bonnet 12 and maintains it in position within a threaded stem mount 18. A cylindrical hole 22 is formed in the side of bonnet nut 10 and is alignable with a cylindrical blind hole 20 (of similar size) formed in the side of bonnet 12. As indicated, a pry bar 24, or similar tool, may be inserted in both holes 22 and 20 to turn bonnet nut 10 and bonnet 12 together to break bonnet 12 loose from stem mount 18. This prior art solution is awkward in that the holes 20 and 22 must be aligned before the pry bar can be used and there is no way to lever the bonnet 12 loose, apart from turning it with bonnet nut 10.